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The Arctic Circle, roughly 67° north of the Equator, defines the boundary of the Arctic waters and lands. The Arctic Circle is one of the two polar circles, and the most northerly of the five major circles of latitude as shown on maps of Earth at about 66° 34' N. [ 1] Its southern equivalent is the Antarctic Circle .
The concept was originally popularized by a map posted on Reddit in 2013, made by a Texas ESL teacher named Ken Myers, whose username on the site gave the figure its name. Myers's original circle covers only about 10% of the Earth's total surface area, with a radius of around 4,000 kilometers (2,500 mi), centered in the South China Sea.
The area of a regular polygon is half its perimeter multiplied by the distance from its center to its sides, and because the sequence tends to a circle, the corresponding formula–that the area is half the circumference times the radius–namely, A = 1 2 × 2πr × r, holds for a circle.
This circle maps to a circle under stereographic projection. So the projection lets us visualize planes as circular arcs in the disk. Prior to the availability of computers, stereographic projections with great circles often involved drawing large-radius arcs that required use of a beam compass. Computers now make this task much easier.
Incircle and excircles. Incircle and excircles of a triangle. In geometry, the incircle or inscribed circle of a triangle is the largest circle that can be contained in the triangle; it touches (is tangent to) the three sides. The center of the incircle is a triangle center called the triangle's incenter. [1] An excircle or escribed circle [2 ...
The area of an annulus is the difference in the areas of the larger circle of radius R and the smaller one of radius r: = = (). As a corollary of the chord formula, the area bounded by the circumcircle and incircle of every unit convex regular polygon is π /4
On the ellipsoid or on spherical projection, all circles of latitude are rhumb lines, except the Equator. The latitude of the circle is approximately the angle between the Equator and the circle, with the angle's vertex at Earth's centre. The Equator is at 0°, and the North Pole and South Pole are at 90° north and 90° south, respectively.
The Twelve-Mile Circle is an approximately circular arc that forms most of the boundary between Delaware and Pennsylvania. It is a combination of different circular arcs that have been feathered together. [1] [2] It is nominally a circle with an approximate and variable 12-mile (19 km) radius, [3] centered in the town of New Castle, Delaware.